5.4-stable review patch. If anyone has any objections, please let me know.
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From: Matthew Brost matthew.brost@intel.com
commit 8af39ec5cf2be522c8eb43a3d8005ed59e4daaee upstream.
A small race exists between spsc_queue_push and the run-job worker, in which spsc_queue_push may return not-first while the run-job worker has already idled due to the job count being zero. If this race occurs, job scheduling stops, leading to hangs while waiting on the job’s DMA fences.
Seal this race by incrementing the job count before appending to the SPSC queue.
This race was observed on a drm-tip 6.16-rc1 build with the Xe driver in an SVM test case.
Fixes: 1b1f42d8fde4 ("drm: move amd_gpu_scheduler into common location") Fixes: 27105db6c63a ("drm/amdgpu: Add SPSC queue to scheduler.") Cc: stable@vger.kernel.org Signed-off-by: Matthew Brost matthew.brost@intel.com Reviewed-by: Jonathan Cavitt jonathan.cavitt@intel.com Link: https://lore.kernel.org/r/20250613212013.719312-1-matthew.brost@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/drm/spsc_queue.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/include/drm/spsc_queue.h +++ b/include/drm/spsc_queue.h @@ -70,9 +70,11 @@ static inline bool spsc_queue_push(struc
preempt_disable();
+ atomic_inc(&queue->job_count); + smp_mb__after_atomic(); + tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next); WRITE_ONCE(*tail, node); - atomic_inc(&queue->job_count);
/* * In case of first element verify new node will be visible to the consumer